BACKGROUND OF THE INVENTION
[0001] Implants adapted for use in the lumbar spine and the thoracic spine become much less
usable in the cervical spine because of differences in anatomy. In the lumbar spine,
the disc spaces are about 25% as tall as the vertebral bodies (i.e., the vertebral
bodies are generally four times taller than the intervening disc space). In the cervical
spine, the disc space can be 50% of the height of the vertebral bodies. The disc spaces
in the cervical spine are generally not greater than 7 or 8 mm tall in most people.
[0002] Screws generally used to secure an implant in the cervical spine typically have a
diameter of between 4 and 5 mm. If two bone screws were to be inserted one each into
each of the adjacent cervical vertebral bodies; and if one were to attempt to vertically
oppose those two bone screws, this would not prove possible because the sum of the
screw diameters would exceed the height of the implant. Such vertically aligned bone
screws would require at least 10 mm of combined height for themselves plus sufficient
implant structure and further height sufficient to surround and retain them. Thus,
altogether the two bone screws and the surrounding implant would have to have a combined
height that would substantially exceed the height of the disc space and an implant
adapted to fit therein.
[0003] Alternatively, one could try to place a number of bone screws more horizontally (side-by-side)
so as to avoid the problems described above associated with vertical alignment. To
provide for the preferred implant stability that the use of paired screws would provide
(two each into each of the adjacent vertebral bodies), one could horizontally align
four bone screws on the equator of the implant with two of the bone screws directed
toward one of the cervical vertebral bodies and two of the bone screws directed toward
the other of the adjacent cervical vertebral bodies. Four such horizontally aligned
bone screws having a head diameter of 5 mm each would require at least 20 mm for the
screw heads alone. Further, with sufficient implant structure to surround each of
those screw heads, the implant width would at a minimum be about 24 mm, which would
exceed the desirable implant width for most cervical disc spaces. Staggering the bone
screw receiving holes would be of some benefit, but of itself not an adequate solution
to the problem described where it is desirable to maintain some symmetry of the screws
to each other, the vertebrae, and the implant.
[0004] One prior art solution to the aforementioned problem teaches extending the height
of the trailing end of the implant to make it taller than the disc space. An example
of this is a flanged implant. The flanged implant makes it possible to place screws
so that they can be vertically aligned and have sufficient structure of the implant
to retain them. The flanged portion of the implant, however, extends outside of the
disc space which may not be desirable in all circumstances. Further, these flanged
implants may not be usable when it is needed to fuse multiple levels of the spine.
[0005] Accordingly, there exists a need for a spinal implant adapted to provide the advantages
of a flanged implant for placement and orientation of bone screws associatated therewith
but without the flanged portion, or the necessity of the implant extending outside
of the disc space.
SUMMARY OF THE INVENTION
[0006] The present invention is directed to an interbody spinal implant, such as but not
limited to a spinal fusion implant, spacers, motion preserving implants, or others.
The implant has opposed upper and lower surfaces, one each for contacting each of
the opposed vertebral bodies adjacent a disc space. The implant is adapted to cooperatively
receive at least two opposed bone screws, at least one screw each for insertion into
each of the vertebral bodies adjacent a disc space. The interbody spinal implant is
adapted to receive the bone screws through its trailing end and to allow for the passage
of the leading end of the bone screws through at least a portion of the implant and
out of the opposed upper or lower implant surfaces, one each respectively. The bone
screws have a leading end, a shaft, threading upon the shaft, and a trailing end.
The implant and the trailing end of the bone screw are adapted to cooperatively engage
each other so as to prevent the further advance of the bone screws through the implant.
At least a portion of the perimeter of the trailing ends of at least some of the bone
screws protrude beyond at least one of the opposed upper or lower implant surfaces.
[0007] In one preferred embodiment, the trailing end is configured to permit a portion of
the head of at least one bone screw to protrude beyond the height of the perimeter
of the trailing end. The trailing end of the implant includes at least one bone screw
receiving opening or hole that has a gap in the perimeter thereof for permitting at
least a portion of the trailing end of a bone screw to protrude beyond the opposed
upper or lower vertebral body engaging surfaces. The gap interrupts the perimeter
of the bone screw receiving hole, so that the bone screw receiving hole has an incomplete
perimeter or C-shape. The gap is sized such that it is less than half the diameter
of the screw. By allowing the screws to each protrude over either the upper or lower
edges of the implant trailing end, the upper and lower screws may be placed such that
the maximum height of the implant trailing end is less than the sum of the maximum
diameter of two bone screws adapted to be inserted in the bone screw receiving holes.
This permits the use of larger bone screws in the trailing end of the implant than
would otherwise be possible. Further, though not so limited, the present invention
allows bone screws of the optimal diameter to be inserted into and in part through
the implant and into the adjacent vertebral bodies without the necessity of a portion
of the implant itself extending beyond the disc space and outside of the spine.
[0008] The trailing end of the implant is configured to permit the bone screws for insertion
into each of the adjacent vertebrae to be angled relative to each other, the implant
trailing end, and to the implant upper and lower surfaces. The opposed bone screws
preferably pull the anterior aspects of the vertebral bodies together toward the implant.
The bone screws preferably penetrate into a portion of the vertebral body closest
to the disc space into which the implant is being installed so as not to interfere
with bone screws from a second implant being installed in an adjacent disc space where
consecutive levels of the spine are being fused. In a preferred embodiment, the trailing
end is configured to lag the bone screws so as to compress the vertebral bodies together
and to load the vertebral body implant interface to promote fusion.
[0009] In certain preferred embodiments, the screws subtend an angle with the upper and
lower surfaces so as to keep them confined to the lower half of the vertebral body
above or the upper half of the vertebral body below the disc space to be fused.
[0010] In other preferred embodiments, the trailing end of the implant is configured to
allow screws that are originating at or close to the vertical midline of the trailing
end of the implant to be directed outward, or divergently oriented; and screws that
originate further from the vertical midline of the trailing end of the implant to
be directed inward, or convergently oriented. The screws that are convergently oriented
are directed to one vertebral body and the screws that are divergently oriented are
directed to the other adjacent vertebral body. Such an arrangement permits such implants
when inserted into adjoining disc spaces to have convergently oriented screws from
one implant and divergently oriented screws from the other implant to be screwed into
the same vertebral body and ensure that the screws do not interfere with one another.
Such a configuration allows screws from different implants to pass each other within
a vertebral body where both adjacent disc spaces are to be fused.
[0011] In any of these embodiments it is preferred though not required that the screws be
retained to the implant by "locking mechanisms" which may include any of those known
to those skilled in the art including, but not limited to, those taught by applicant,
for example,
U.S. Patent No. 6,139,550, titled "Skeletal Plating System,"
U.S. Application Serial No. 09/022,293 titled "Anterior Cervical Plating System, Instrumentation, and Method of Installation,"
and
U.S. Application Serial No. 09/565,392 titled "Interbody Spinal Fusion Implants with Opposed Locking Screws", all of which
are incorporated herein by reference. The trailing end of the implant may be configured
to receive bone screws such that they are constrained within the bone screw receiving
holes (i.e., fixing the trajectory of each bone screw), or left unconstrained within
the bone screw receiving holes for allowing variable screw angles. If a locking mechanism
is used, the screws may start out constrained within the bone screw receiving holes
and remain so when locked. Alternatively, the screws may start out unconstrained prior
to locking them, and upon being locked, may be constrained by the screw lock or left
unconstrained by the screw lock. Examples are described below.
[0012] If it is desired to have the bone screws constrained in the bone screw receiving
holes then the bone screw receiving holes may be adapted to capture the screws. Preferably,
an interference fit is formed between the wall of the bone screw receiving hole and
the screw to prevent the screws from moving within the bone screw receiving hole.
[0013] The screws may also be self-locking with cooperative mating threads between the screw
head and the bone screw receiving hole. An example of a preferred self-locking bone
screw may be found in applicant's Application Serial No. 09/565,392 titled "Spinal
Implant with Vertebral Endplate Engaging Anchor" incorporated herein by reference.
[0014] If it is desired that the bone screws are unconstrained then the bone screws may
have a rounded head portion and/or a reduced neck diameter to permit movement of the
bone screws so as to allow the angle between the implant and the bone screw to be
variable.
[0015] If it is desired to lock the bone screw, the locking mechanism may be adapted to
leave the bone screw constrained or unconstrained by adapting the interior surface
of the locking mechanism accordingly. For example, the end of a screw lock facing
a screw head may be concave to accommodate a round screw head, thereby allowing an
unconstrained screw to be locked to the implant, yet still permit variable screw angles
relative to the implant. Alternatively, the locking mechanism may be configured to
constrain an unconstrained bone screw by having the lock forcefully bear upon the
screw head.
[0016] Although bone screw locks are preferred, the invention is not so limited. Bone screws
need not be locked to the implant, but simply may have, for example, a stop or shoulder
for stopping the progress of a bone screw through the implant beyond a certain point
along the bone screw length.
[0017] The bone screw heads are preferably but not necessarily flush or slightly below the
exterior surface of the trailing end of the implant when fully installed so as not
to substantially protrude therefrom as into delicate anatomical structures that may
be present proximate the exterior surface of the trailing end of the implant.
[0018] The implant of the present invention is useful throughout the spine, including the
cervical, thoracic, and lumbar portions, and depending upon the location, may be inserted
from the anterior, posterior, or lateral aspects of the spine.
[0019] Many of the preferred embodiments of the present invention have one or more of the
following advantages over the prior art. One advantage is a more shallow screw angle
between the screw and the implant. A more shallow screw angle provides the screws
with additional anchoring force. The ability of the screw to anchor in the bone is
proportional to the amount of threaded surface area. As the screw gets longer, its
bite gets better. Therefore, a more shallow screw angle permits the screw to stay
in a short height body longer.
[0020] Another advantage is that by starting with the screw close to the implant surface
and having the screw exit the implant sooner, less of the screw will be in the implant,
thereby providing more space within the implant for fusion promoting substances or
other desired contents.
[0021] A further advantage is the accommodation of the trailing ends of bone screws within
the depth of the disc space to reduce the risk of damage to adjacent delicate structures,
including but not limited to proximate vascular and neurological structures within
the body. Parts of implants extending beyond the depth of the disc space may have
a risk of damaging these adjacent delicate structures. It should be understood that
the accommodation of the trailing ends of bone screws within the depth of the disc
space is a preferred embodiment only and that the invention is not so limited.
[0022] A further advantage is the ability of the bone screws to exit the implant quicker
and engage an adjacent vertebral body. A trailing end of a bone screw that is closer
to the equator of the implant (i.e., the horizontal mid-line of the trailing end)
and further from the opposed upper or lower surfaces of the implant takes longer for
the threaded portion of the screw to leave the implant. In contrast, the present invention
in one or more preferred embodiments allows the threaded portion of a bone screw to
leave the implant sooner at a shallower angle and to thereby have additional threaded
length than otherwise would be achieved if more of the threaded portion were within
the trailing end of the implant.
[0023] While the above-described configurations are preferred for various advantages they
do not in any way limit the breadth of the present invention, which is limited only
by the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024]
FIG. 1 is a trailing end perspective view of an embodiment of the spinal implant of
the present invention.
FIG. 2 is a top plan view of the spinal implant of FIG. 1.
FIG. 3 is a side elevation view of the spinal implant of FIG. 1.
FIG. 4 is a trailing end elevation view of the spinal implant of FIG. 1.
FIG. 5 is a side elevation view of an embodiment of the spinal implant of the present
invention shown being inserted into an implantation space formed across the disc space
between two adjacent vertebral bodies of the spine shown in partial cross-section.
FIG. 6 is a side elevation view of a drill and drill guide for forming bone screw
receiving openings into adjacent vertebral bodies corresponding to bone screw receiving
holes in the trailing end of the spinal implant of the present invention implanted
between two adjacent vertebral bodies shown in partial cross-section.
FIG. 7 is a top plan view of the spinal implant of FIGS. 1-4 in the inserted position
with bone screws installed and one of the adjacent vertebral bodies shown.
FIG. 8 is a trailing end elevation view of the spinal implant of FIGS. 1-4 installed
between two adjacent vertebral bodies shown in hidden line with the locking mechanisms
in the unlocked position.
FIG. 9 is an exploded view of the spinal implant of FIG. 8 and a driver holder instrument
and locking tool for installing and locking the implant.
FIG. 10 is a top plan view in partial cross-section of the spinal implant of FIG.
8 and bone screws installed between two adjacent vertebral bodies with the driver
holder instrument and locking tool locking one of the locking mechanisms of the implant
in the inserted position with one of the adjacent vertebral bodies shown.
[0025] FIG. 11 is a trailing end elevation view of the spinal implant of FIG. 8 with the
locking mechanisms shown locking all four bone screws to the implant.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Reference will now be made in detail to the present preferred embodiments of this
invention, examples of which are illustrated in the accompanying drawings. Similar
reference numbers such as "102, 202" will be used throughout the drawings to refer
to similar portions of different embodiments of the present invention.
[0027] As shown in FIGS. 1-4, a preferred embodiment of the spinal implant of the present
invention is generally referred to by the numeral 100. As used herein, the term "implant"
includes any device adapted for insertion between two adjacent vertebral bodies, for
example only, spacers, bone dowels, and spinal fusion implants. Implant 100 has a
leading end 102, an opposite trailing end 104, and sides 106 and 108 therebetween
for connecting, spanning, or joining, ends 102, 104.
[0028] In a preferred embodiment, leading end 102 can be a portion of a circle and the implant
width can be equal to that portion of the circle, or if a half circle, then the diameter
of that circle. Alternatively, leading end 102 may be straight at least in part, and
for example the straight part can be at an approximately right angle to sides 106,
108 to form a generally rectangular or square shape. The configuration of the leading
end of the implant of the present invention may be adapted to match the configuration
of an implantation space formed across the disc space and into the adjacent vertebral
bodies in accordance with
U.S. Patent No. 6,159,214 titled "Milling Instrumentation and Method for Preparing a Space Between Adjacent
Vertebral Bodies" and applicant's co-pending patent application Serial No. 09/490,901
titled "Instrument and Method for Creating an Intervertebral Space for Receiving an
Implant,", both of which are incorporated by reference herein.
[0029] Implant 100 has a vertebral body engaging upper surface 110 and an opposite vertebral
body engaging lower surface 112. In a preferred embodiment, upper and lower surfaces
110, 112 may be convergent toward one another such that implant 100 is able to place
the adjacent vertebral bodies in angular relationship to each other, for example,
in lordosis. Upper and lower surfaces 110, 112 may have at least one opening 114 therethrough
for permitting the growth of bone from adjacent vertebral body to adjacent vertebral
body through implant 100.
[0030] Both ends 102 and 104 may include openings such as 116 so as to permit for the growth
of bone and vascular access therethrough. Similarly, sides 106, 108 can include openings
such as 118 for similar or other purposes. Implant 100 preferably has an open interior
120 between sides 106, 108 to permit for the growth of bone from adjacent vertebral
body to adjacent vertebral body therethrough. The implant 100 itself, any of its various
surfaces, open interior 120 and/or any of its openings such as 114, 116, 118, for
example, can be coated with, or contain bone growth promoting materials, including
but not limited to, bone, bone morphogenetic proteins, hydroxyapatite, genes coding
for the production of bone, or any other material that intrinsically participates
in the growth of bone from one of the adjacent vertebral bodies to the other of the
adjacent vertebral bodies at the fusion site.
[0031] In a preferred embodiment, trailing end 104 has an exterior surface 122 and an interior
surface 124. At least exterior surface 122 may be curved to conform to at least a
portion of the natural curvature of the anterior aspect of the vertebral bodies. For
example, exterior surface 122 may be concave in a horizontal plane, in a vertical
plane, or biconcave in both the vertical and horizontal planes. Exterior surface 122
may, but need not, correspond to the configuration of interior surface 124. In the
preferred embodiment, exterior surface 122 is configured to eliminate sharp edges
and corners to protect the adjacent delicate vascular and neurological structures
within the body. For example, exterior surface 122 can be tapered at its exterior
edges and can have rounded corners. The shape of trailing end 104 itself may be generally
quadrilateral, circular, or any other shape useful for the intended purpose.
[0032] Trailing end 104 includes bone screw receiving holes 126 for receiving bone screws
128 for securing implant 100 to the adjacent vertebral bodies. Bone screw receiving
holes 126 include a gap 130 in the perimeter of bone screw receiving holes 126 for
permitting at least a portion of bone screw 128 to protrude beyond perimeter 132 of
trailing end 104. Trailing end 104 may be straight, curved, or anatomically contoured.
Gap 130 interrupts the perimeter of bone screw receiving holes 126, so that bone screw
receiving holes 126 have an incomplete perimeter or C-shape. At least one of the bone
screw receiving holes 126 is adapted to cooperatively engage the trailing end of bone
screw 128 to allow at least a portion of the perimeter of the trailing end of at least
one of the bone screws to protrude beyond at least one of the opposed upper and lower
implant surfaces.
[0033] As used herein, the trailing end of a bone screw includes not less than that portion
of the bone screw at the end opposite the leading end of the screw adapted to cooperatively
engage the implant to prevent its passage therethrough. The trailing end may include
the head and/or shaft proximate to the head, for example, shaft 134 and head 138 as
shown in FIG. 1. The bone screw heads are preferably but not necessarily flush or
slightly below the exterior surface of the trailing end of the implant when fully
installed so as not to protrude therefrom into anatomical structures that may be present
proximate the exterior surface of the trailing end of the implant.
[0034] The trailing end of the implant may be configured to receive bone screws such that
they are constrained within the bone screw receiving holes (i.e., fixing the trajectory
of each bone screw), or left unconstrained within the bone screw receiving holes for
allowing variable screw angles. Preferably, for a constrained configuration an interference
fit is formed between the wall of the bone screw receiving hole and the screw to prevent
the screws from moving within the bone screw receiving hole. Constrained screws may
also be self-locking with cooperative mating threads between the screw head and the
bone screw receiving hole.
[0035] If it is desired that the bone screws are unconstrained then the bone screws may
have a rounded head portion and/or a reduced neck diameter to permit movement of the
bone screws so as to allow the angle between the implant and the bone screw to be
variable.
[0036] Bone screws need not be locked to the implant, but simply may have, for example,
a shoulder for stopping the progress of a bone screw through the implant beyond a
certain point along the bone screw length. It is appreciated that all the bone screws
described herein may be self-tapping. Bone screw receiving holes 126 preferably contain
a recessed portion 136 to accommodate screw head 138 so that screw head 138 does not
substantially protrude away from the trailing end. Gap 130 is sized such that it is
less than half the diameter of screw 128. By allowing screws 128 to protrude over
edges 140, 142 of trailing end 104, upper and lower screws may be placed such that
the maximum height H of trailing end 104 is less than the sum of the maximum diameter
of two bone screws adapted to be inserted in bone screw receiving holes 126.
[0037] Bone screw receiving holes 126 may be adapted to capture screws 128, thereby constraining
the screws within trailing end 104. Alternatively, trailing end 104 can further include
at least one locking mechanism 144 for locking the bone screws to implant 100. Although
bone screw locks are preferred, the invention is not so limited.
[0038] In the various embodiments of the present invention, locking mechanisms 144 and trailing
end 104 may be configured to either rigidly capture bone screws 128 so that their
positions are fixed, or alternatively allow for the screw angles to be variable in
an unconstrained state in which case the screw angles may remain variable when locked.
[0039] Locking mechanism 144 can be in the form of a screw or a rivet having a head for
contacting and securing the bone screws to implant 100. Locking mechanism 144 may
be capable of rotational movement relative to trailing end 104. Locking mechanism
144 includes a tool-engaging portion 146 for moving locking mechanism 144 from an
unlocked to a locked position.
[0040] As best shown in FIGS. 1 and 4, locking mechanism 144 further includes removed portions
148 permitting the installation of bone screws into bone screw receiving holes 126
while locking mechanism 144 is in the unlocked position. In a preferred embodiment,
locking mechanisms 144 can turn 180 degrees to be fully tightened. Locking mechanisms
144 can turn in the same direction or counter to one another. The bottom of the head
of locking mechanism 144 can be of various shapes and, for example, can be ramped
or concave. Further, as taught in applicant's Application Serial No.
09/565,392 titled "Spinal Implant with Vertebral Endplate Engaging Anchor", the present invention
may be adapted to receive self-locking screws.
[0041] Locks 144 can work either to constrain screws 128 by fixing their positions, or in
the alternative by preventing screws 128 from backing out without fixing the screws
position so that the screws can allow for settling of the disc space (dynamization).
[0042] It is appreciated that the present invention includes the use of other screw locking
mechanisms and devices such as would be used in other plate/screw or implant/screw
devices and as would be known to one of ordinary skill in the art.
[0043] As shown in FIG. 9, trailing end 104 further includes alignment holes 150, 152 and
threaded engagement hole 153 for engaging alignment pegs 154 and threaded driver 155,
respectively from a driver instrument described below. Any other means of engaging
the implant to assist in its insertion as would be known in the art is within the
scope of the present invention.
[0044] A preferred origin and trajectory of bone screw receiving hole 126 is such that a
surgeon can (but does not necessarily have to be able to) insert bone screws 128 through
holes 126 to an optimal or desired depth without those bone screws crossing a plane
bisecting the height of the adjacent vertebral body. An alternative embodiment may
include top and bottom screws that are placed asymmetrically so as to be offset from
one another so that the screws from such implants inserted into adjacent disc spaces
pass each other in an intermediate vertebral body without hitting one another. For
example, an implant may have two bone screws in the trailing end toward the outer
sides and projecting through the upper surface and one bone screw in the middle of
the trailing end projecting through the lower surface.
[0045] As shown in FIG. 5, implant 100 is inserted into an implantation space formed across
the disc space into the adjacent vertebral bodies. Implant 100 is installed with leading
end 102 inserted first into the disc space.
[0046] As shown in FIG. 6, bone screw receiving holes 126 may be formed into the adjacent
vertebral bodies with a drill 156 and a drill guide 158, an awl, or other device.
Drill 156 has a bone removing end 160 and a shaft 162. Drill guide 158 has a leading
end 164 adapted for insertion into one of bone screw receiving holes 126 of trailing
end 104. Leading end 164 has a smaller dimension 166, a larger dimension 168, and
a shoulder 170 corresponding to the reduced dimension portions of bone screw receiving
holes 126 that are configured to receive the head portion of bone screws 128. Drill
guide 158 has an inner bore (not shown) that in one preferred embodiment is aligned
with the central longitudinal axis of the bone screw receiving holes 126 when leading
end 164 is properly seated therein. If it is desired to vary the angle of drill guide
158 to bone screw receiving holes 126, the tip of drill guide 158 may be rounded.
In the alternative, the drill guide may screw into the bone screw receiving hole,
or may attach to the implant by any other technique known in the art. Further, the
openings into the bone may be formed with a spike or other device, or the screws may
be inserted without first forming bores into the bone.
[0047] When drill guide 158 is seated within bone screw receiving hole 126, drill 156 passes
through the inner bore to form a bone screw receiving opening into the bone of the
adjacent vertebral bodies corresponding in alignment to bone screw receiving holes
126. In the preferred embodiment, bone screw receiving openings 126 are formed in
the bone located at or proximate the junction of the two cortices of the vertebral
bodies.
[0048] In the spinal implant of the present invention, the bone screws can be oriented in
an angular relationship to each other so as to be divergent along the vertical plane
of the implant when installed into the adjacent vertebral bodies. The preferred angular
divergence from the implant surface is preferably 25°-40°, but any angle useful for
the intended purpose is within the scope of the present invention. In a preferred
embodiment, screws 128 are angled such that they do not extend beyond half the height
of the adjacent vertebral body. This ensures that screws of one implant will not contact
the screws of an implant inserted in a neighboring disc space.
[0049] In the implant of the present invention, if lag screws are utilized or if there is
a lagging implant to screw relationship, then the adjacent vertebral bodies are pulled
toward implant 100 as bone screws 128 are installed into the vertebral bone to create
a compressive load on the implant. Further, the angling of bone screws 128, keeps
the anterior portion of the adjacent vertebral bodies together during extension movement
of the spine such as would occur when a patient leans backwards. Among the many advantages
of the present invention, the anterior portions of the vertebral bodies adjacent implant
100 do not move apart as they are held in place by bone screws 128 inserted through
trailing end 104, the back of the implant is not driven into the vertebral bodies
with spinal extension, and the compressive load is safely distributed over the entire
length of the interbody portion of the implant.
[0050] FIG. 7 shows a top plan view of implant 100 installed within the disc space between
two adjacent vertebral bodies and bone screws 128 installed in trailing end 104. In
a preferred embodiment, bone screws 128 are toed-in toward each other. It is appreciated,
however, that bone screws 128 need not be toed-in but may be parallel, diverging,
or have any other desired orientation to one another. It is further appreciated that
only a single screw or three or more screws can be used to secure the implant to each
of the adjacent vertebral bodies instead of the two screws shown in FIG. 7.
[0051] FIG. 8 is a trailing end elevation view of spinal implant 100 installed between two
adjacent vertebral bodies with locking mechanisms 144 shown in the unlocked position
and bone screws 128 in place. Upper bone screws 128 are converging while lower bone
screws 128 are diverging. If two such implants are placed into consecutive disc spaces,
converging upper bone screws 128 of one implant and diverging lower bone screws 128
of the other implant would not interfere with each other because of the difference
in angulation of the respective bone screws.
[0052] As shown in FIG. 9, implant 100 can be installed with driver instrumentation 172
for both holding the implant so as to be useful for insertion and for preventing torquing
of the implant when the locks are secured in their locked position. Driver instrumentation
172 has a blocker portion 174 for cooperatively engaging trailing end 104 of implant
100. Blocker 174 has a leading arcuate surface 176 that may be configured to conform
at least in part to the contour of trailing end 104. Driver instrumentation 172 has
a shaft 178 extending from blocker 174 with of an inner bore 180 along the longitudinal
axis of shaft 178. Extending from blocker 174 are a pair of alignment pegs 154 and
threaded driver shaft 155 for cooperatively engaging alignment holes 150, 152 and
threaded hole 153, respectively, in trailing end 104. Blocker 174 has openings 182
that are coaxially aligned with locking mechanisms 144, respectively. Openings 182
are configured to receive a locking tool 184 therethrough for accessing and operating
locking mechanisms 144. Instrumentation 172 allows the surgeon to tighten locking
mechanisms 144 against the blocker 174 instead of torquing the spine of the patient.
[0053] Driver instrument 172 and blocker 174 are shown as an example of insertion instrumentation
with the understanding that any inserter or a blocker or combined inserter and blocker
known to one of ordinary skill in the art and useful for the intended purpose is within
the scope of the present invention.
[0054] FIG. 10 shows a top plan view in partial cross-section of spinal implant 100 installed
between two adjacent vertebral bodies and coupled to the driver instrumentation 172
with tool 184 (such as a screw driver) shown locking the locking mechanism 144 (a
rivet) to secure bone screws 128 to trailing end 104. It is appreciated that locking
mechanism 144 could be a rivet, screw, or the like.
[0055] FIG. 11 is a trailing end elevation view of spinal implant 100 installed between
two adjacent vertebral bodies with locking mechanisms 144 shown in the locked position
in the direction of the arrows to lock bone screws 128 to trailing end 104. It should
be understood that either clockwise or counter-clockwise rotational direction can
be used for locking screws 128.
[0056] Further preferred embodiments of the present invention are given in the following
paragraphs:
A first further preferred embodiment of the present invention is a spinal implant
for insertion between adjacent vertebral bodies, comprising: opposed upper and lower
surfaces adapted to contact each of the adjacent vertebral bodies, respectively from
within the disc space; a leading end for insertion between the adjacent vertebral
bodies; a trailing end opposite said leading end, said trailing end having an exterior
surface and an outer perimeter with an upper edge and a lower edge adapted to be oriented
toward the adjacent vertebral bodies, respectively; and a plurality of bone screw
receiving holes in said trailing end, at least one of which is adapted to only partially
circumferentially surround a trailing end of a bone screw adapted to be received therein,
at least one of said bone screw receiving holes passing through said exterior surface
and one of said edges so as to permit the trailing end of the bone screw to protrude
beyond said one of said edges.
In a first aspect of the first further preferred embodiment of the present invention,
said implant is a fusion implant.
In a second aspect of the first further preferred embodiment of the present invention,
a plane of said trailing end is curved.
In a third aspect of the first further preferred embodiment of the present invention,
said implant has a height equal to the distance between the adjacent vertebral bodies
where installed into the disc space when installed.
In a fourth aspect of the first further preferred embodiment of the present invention,
said outer perimeter of said trailing end has at least one gap therein for permitting
a portion of at least an outer diameter of a bone screw to protrude beyond said outer
perimeter of said trailing end, said gap in said bone screw receiving hole dimensioned
to be less than the outer diameter of the bone screw.
In a fifth aspect of the first further preferred embodiment of the present invention,
at least one of said bone screw receiving holes passing through said exterior surface
and one of said edges is C-shaped in cross section.
In a sixth aspect of the first further preferred embodiment of the present invention,
at least one of said bone screw receiving holes passing through said exterior surface
and one of said edges has a partial circumference intersecting with the outer perimeter
of said trailing end.
In a seventh aspect of the first further preferred embodiment of the present invention,
said trailing end is relieved to allow for a head of a bone screw inserted into one
of said bone screw receiving holes to be at least partially recessed.
In an eighth aspect of the first further preferred embodiment of the present invention,
at least two of said plurality of bone screw receiving holes are at different distances
from the mid-longitudinal axis of said implant.
In a ninth aspect of the first further preferred embodiment of the present invention,
said trailing end is generally quadrilateral in shape.
In a tenth aspect of the first further preferred embodiment of the present invention,
at least one pair of said plurality of bone screw receiving holes are adapted to orient
bone screws to be received therein at an angle to a horizontal mid-longitudinal plane
of said implant passing through said leading and trailing ends.
In an eleventh aspect of the first further preferred embodiment of the present invention,
said plurality of bone screw receiving holes includes a pair of screw receiving holes
along said upper edge and a pair of screw receiving holes along said lower edge, one
of said pair of bone screw receiving holes being adapted to position bone screws in
a convergent relationship to one another. The other of said pair of bone screw receiving
holes may be adapted to position bone screws in a divergent relationship to one another.
Said angle may be greater than 15 degrees and less than 60 degrees.
In a twelfth aspect of the first further preferred embodiment of the present invention,
said implant further comprises at least one lock for retaining a bone screw within
said implant. Said at least one lock may retain a plurality of bone screws to said
implant.
In a 13th aspect of the first further preferred embodiment of the present invention, said implant
further comprises at least one bone screw having a leading end for placement in the
vertebral body and a trailing end opposite said leading end adapted to cooperatively
engage said implant so as to prevent the further advancement of the screw into the
bone and to be retained within one of said plurality of bone screw receiving holes
of said implant.
In a 14th aspect of the first further preferred embodiment of the present invention, said implant
comprises one of bone and bone growth promoting material. Said bone growth promoting
material may be selected from one of bone morphogenetic protein, hydroxyapatite, and
genes coding for the production of bone.
In a 15th aspect of the first further preferred embodiment of the present invention, said implant
is treated with a bone growth promoting substance.
In a 16th aspect of the first further preferred embodiment of the present invention, said implant
comprises at least one of the following materials: metal, titanium, plastic, and ceramic.
In a 17th aspect of the first further preferred embodiment of the present invention, said implant
is formed of a porous material.
In an 18th aspect of the first further preferred embodiment of the present invention, said implant
has an interior surface and a hollow defined therein, said hollow being capable of
containing bone growth promoting material. Said bone growth promoting material may
be selected from one of bone morphogenetic protein, hydroxyapatite, and genes coding
for the production of bone.
In a 19th aspect of the first further preferred embodiment of the present invention, said implant
is in combination with a chemical substance to inhibit scar formation.
A second further preferred embodiment of the present invention is a spinal implant
for insertion between adjacent vertebral bodies, comprising: opposed upper and lower
surfaces adapted to contact one each of the adjacent vertebral bodies from within
the disc space; a leading end for insertion between the adjacent vertebral bodies;
and a trailing end opposite said leading end, said trailing end having an upper edge
and a lower edge, said trailing end being adapted to only partially circumferentially
surround the circumference of at least one bone screw adapted to be received therein.
In a first aspect of the second further preferred embodiment of the present invention,
said implant is a fusion implant.
In a second aspect of the second further preferred embodiment of the present invention,
said trailing end is curved.
In a third aspect of the second further preferred embodiment of the present invention,
said implant has a height equal to the distance between the adjacent vertebral bodies
where installed into the disc space when installed.
In a fourth aspect of the second further preferred embodiment of the present invention,
at least one of said upper and lower edges of said trailing end has at least one gap
therein for permitting a portion of at least an outer diameter of a bone screw to
protrude beyond said at least one of said upper and lower edges of said trailing end,
said gap being dimensioned to be less than the outer diameter of the bone screw.
In a fifth aspect of the second further preferred embodiment of the present invention,
said trailing end is relieved to allow for a head of a bone screw inserted into said
trailing end to be at least partially recessed.
In a sixth aspect of the second further preferred embodiment of the present invention,
said trailing end is adapted to orient bone screws to be received therein at an angle
to a horizontal mid-longitudinal plane of said implant passing through said leading
and trailing ends. Said trailing end may have a pair of screw receiving holes along
said upper edge and a pair of screw receiving holes along said lower edge, one of
said pair of bone screw receiving holes being adapted to position bone screws in a
convergent relationship to one another. The other of said pair of bone screw receiving
holes may be adapted to position bone screws in a divergent relationship to one another.
In a seventh aspect of the second further preferred embodiment of the present invention,
said implant further comprises at least one lock for retaining a bone screw within
said implant. Said at least one lock may retain a plurality of bone screws to said
implant.
In an eighth aspect of the second further preferred embodiment of the present invention,
said implant further comprises at least one bone screw having a leading end for placement
in the vertebral body and a trailing end opposite said leading end adapted to cooperatively
engage said implant so as to prevent the further advancement of the screw into the
bone and to be retained within said trailing end of said implant.
In a ninth aspect of the second further preferred embodiment of the present invention,
said implant comprises one of bone and bone growth promoting material. Said bone growth
promoting material may be selected from one of bone morphogenetic protein, hydroxyapatite,
and genes coding for the production of bone.
In a tenth aspect of the second further preferred embodiment of the present invention,
said implant comprises at least one of the following materials:
metal, titanium, plastic, and ceramic.
[0057] In an eleventh aspect of the second further preferred embodiment of the present invention,
said implant has an interior surface and a hollow defined therein, said hollow being
capable of containing bone growth promoting material. Said bone growth promoting material
may be selected from one of bone morphogenetic protein, hydroxyapatite, and genes
coding for the production of bone.
[0058] In a twelfth aspect of the second further preferred embodiment of the present invention,
said implant is in combination with a chemical substance to inhibit scar formation.
[0059] A third further preferred embodiment of the present invention is a spinal implant
for insertion between adjacent vertebral bodies, comprising: opposed upper and lower
portions adapted to contact each one of the adjacent vertebral bodies from within
the disc space; a leading end for insertion between the adjacent vertebral bodies;
and a trailing end opposite said leading end, said trailing end having an upper edge,
a lower edge, and a maximum height therebetween, said trailing end being adapted to
receive at least a portion of a bone screw passing therein that extends beyond said
maximum height immediately adjacent thereto.
[0060] In a first aspect of the third further preferred embodiment of the present invention,
said implant is a fusion implant.
[0061] In a second aspect of the third further preferred embodiment of the present invention,
said trailing end is curved.
[0062] In a third aspect of the third further preferred embodiment of the present invention,
said implant has a height equal to the distance between the adjacent vertebral bodies
where installed into the disc space when installed.
[0063] In a fourth aspect of the third further preferred embodiment of the present invention,
at least one of said upper and lower edges of said trailing end has at least one gap
therein for permitting a portion of at least an outer diameter of a bone screw to
protrude beyond said at least one of said upper and lower edges of said trailing end,
said gap being dimensioned to be less than the outer diameter of the bone screw.
[0064] In a fifth aspect of the third further preferred embodiment of the present invention,
said trailing end is relieved to allow for a head of a bone screw inserted into said
trailing end to be at least partially recessed.
[0065] In a sixth aspect of the third further preferred embodiment of the present invention,
said trailing end is adapted to orient bone screws to be received therein at an angle
to a horizontal mid-longitudinal plane of said implant passing through said leading
and trailing ends. Said trailing end may have a pair of screw receiving holes along
said upper edge and a pair of screw receiving holes along said lower edge, one of
said pair of bone screw receiving holes being adapted to position bone screws in a
convergent relationship to one another. The other of said pair of bone screw receiving
holes may be adapted to position bone screws in a divergent relationship to one another.
[0066] In a seventh aspect of the third further preferred embodiment of the present invention,
said implant further comprises at least one lock for retaining a bone screw within
said implant. Said at least one lock may retain a plurality of bone screws to said
implant.
[0067] In an eighth aspect of the third further preferred embodiment of the present invention,
said implant further comprises at least one bone screw having a leading end for placement
in the vertebral body and a trailing end opposite said leading end adapted to cooperatively
engage said implant so as to prevent the further advancement of the screw into the
bone and to be retained within said trailing end of said implant.
[0068] In a ninth aspect of the third further preferred embodiment of the present invention,
said implant comprises one of bone and bone growth promoting material. Said bone growth
promoting material may be selected from one of bone morphogenetic protein, hydroxyapatite,
and genes coding for the production of bone.
[0069] In a tenth aspect of the third further preferred embodiment of the present invention,
said implant comprises at least one of the following materials: metal, titanium, plastic,
and ceramic.
[0070] In an eleventh aspect of the third further preferred embodiment of the present invention,
said implant has an interior surface and a hollow defined therein, said hollow being
capable of containing bone growth promoting material. Said bone growth promoting material
may be selected from one of bone morphogenetic protein, hydroxyapatite, and genes
coding for the production of bone.
[0071] In a twelfth aspect of the third further preferred embodiment of the present invention,
said implant is in combination with a chemical substance to inhibit scar formation.
[0072] A fourth further preferred embodiment of the present invention is a spinal implant
for insertion between adjacent vertebral bodies, comprising: opposed upper and lower
surfaces adapted to contact each one of the adjacent vertebral bodies from within
the disc space; a leading end for insertion between the adjacent vertebral bodies;
and a trailing end opposite said leading end, said trailing end having a plurality
of bone screw receiving holes, an upper edge, a lower edge, and a maximum height therebetween,
said maximum height of said trailing end being adapted to be less than the sum of
the maximum diameter of two bone screws adapted to be inserted in said bone screw
receiving holes, said bone screw receiving holes being adapted to incompletely circumferentially
receive at least one of the bone screws.
[0073] In a first aspect of the fourth further preferred embodiment of the present invention,
said implant is a fusion implant.
[0074] In a second aspect of the fourth further preferred embodiment of the present invention,
said trailing end is curved.
[0075] In a third aspect of the fourth further preferred embodiment of the present invention,
said implant has a height equal to the distance between the adjacent vertebral bodies
where installed into the disc space when installed.
[0076] In a fourth aspect of the fourth further preferred embodiment of the present invention,
at least one of said upper and lower edges of said trailing end has at least one gap
therein for permitting a portion of at least an outer diameter of a bone screw to
protrude beyond said at least one of said upper and lower edges of said trailing end,
said gap in said bone screw receiving hole dimensioned to be less than the outer diameter
of the bone screw.
[0077] In a fifth aspect of the fourth further preferred embodiment of the present invention,
at least one of said bone screw receiving holes is C-shaped in cross section.
[0078] In a sixth aspect of the fourth further preferred embodiment of the present invention,
said trailing end is relieved to allow for a head of a bone screw inserted into one
of said bone screw receiving holes to be at least partially recessed.
[0079] In a seventh aspect of the fourth further preferred embodiment of the present invention,
at least one pair of said plurality of bone screw receiving holes are adapted to orient
bone screws to be received therein at an angle to a horizontal mid-longitudinal plane
of said implant passing through said leading and trailing ends. Said plurality of
bone screw receiving holes may include a pair of screw receiving holes along said
upper edge and a pair of screw receiving holes along said lower edge, one of said
pair of bone screw receiving holes being adapted to position bone screws in a convergent
relationship to one another. The other of said pair of bone screw receiving holes
may be adapted to position bone screws in a divergent relationship to one another.
[0080] In an eight aspect of the fourth further preferred embodiment of the present invention,
said implant further comprises at least one lock for retaining a bone screw within
said implant. Said at least one lock may retain a plurality of bone screws to said
implant.
[0081] In a ninth aspect of the fourth further preferred embodiment of the present invention,
said implant further comprises at least one bone screw having a leading end for placement
in the vertebral body and a trailing end opposite said leading end adapted to cooperatively
engage said implant so as to prevent the further advancement of the screw into the
bone and to be retained within one of said plurality of bone screw receiving holes
of said implant.
[0082] In a tenth aspect of the fourth further preferred embodiment of the present invention,
said implant comprises one of bone and bone growth promoting material. Said bone growth
promoting material may be selected from one of bone morphogenetic protein, hydroxyapatite,
and genes coding for the production of bone.
[0083] In an eleventh aspect of the fourth further preferred embodiment of the present invention,
said implant comprises at least one of the following materials:
metal, titanium, plastic, and ceramic.
[0084] In a twelfth aspect of the fourth further preferred embodiment of the present invention,
said implant has an interior surface and a hollow defined therein, said hollow being
capable of containing bone growth promoting material. Said bone growth promoting material
may be selected from one of bone morphogenetic protein, hydroxyapatite, and genes
coding for the production of bone.
[0085] In a 13
th aspect of the fourth further preferred embodiment of the present invention, said
implant is in combination with a chemical substance to inhibit scar formation.
[0086] A fifth further preferred embodiment of the present invention is a spinal fusion
implant for insertion between adjacent vertebral bodies, comprising: an implant having:
opposed upper and lower surfaces adapted to contact each of the opposed adjacent vertebral
bodies from within the disc space; a leading end for insertion between the adjacent
vertebral bodies; a trailing end opposite said leading end, said trailing end having
an exterior surface and an outer perimeter with an upper edge and a lower edge adapted
to be oriented toward the adjacent vertebral bodies, respectively; and a plurality
of bone screw receiving holes in said trailing end, at least one of which is adapted
to only partially circumferentially surround the trailing end of a bone screw adapted
to be received therein, at least one of said screw receiving holes passing through
said exterior surface and one of said edges so as to permit the bone screw to protrude
over one of said edges within a plane of said trailing end; and at least one bone
screw, said screw having:
a leading end for placement in the vertebral body; and opposite, a trailing end adapted
to cooperatively engage said implant so as to prevent the further advancement of the
screw into the bone and to be retained within said implant.
[0087] In a first aspect of the fifth further preferred embodiment of the present invention,
said implant is a fusion implant.
[0088] In a second aspect of the fifth further preferred embodiment of the present invention,
said plane of said trailing end is curved.
[0089] In a third aspect of the fifth further preferred embodiment of the present invention,
said implant has a height equal to the distance between the adjacent vertebral bodies
where installed into the disc space when installed.
[0090] In a fourth aspect of the fifth further preferred embodiment of the present invention,
said outer perimeter of said trailing end has at least one gap therein for permitting
a portion of at least an outer diameter of a bone screw to protrude beyond the outer
perimeter of said trailing end, said gap in said bone screw receiving hole dimensioned
to be less than the outer diameter of the bone screw.
[0091] In a fifth aspect of the fifth further preferred embodiment of the present invention,
at least one of said bone screw receiving holes passing through said exterior surface
and one of said edges is C-shaped in cross section.
[0092] In a sixth aspect of the fifth further preferred embodiment of the present invention,
at least one of said bone screw receiving holes passing through said exterior surface
and one of said edges has a partial circumference intersecting with the outer perimeter
of said trailing end.
[0093] In a seventh aspect of the fifth further preferred embodiment of the present invention,
said trailing end is relieved to allow for a head of a bone screw inserted into one
of said bone screw receiving holes to be at least partially recessed.
[0094] In an eighth aspect of the fifth further preferred embodiment of the present invention,
at least one pair of said plurality of bone screw receiving holes are adapted to orient
bone screws to be received therein at an angle to a horizontal mid-longitudinal plane
of said implant passing through said leading and trailing ends. Said plurality of
bone screw receiving holes may include a pair of screw receiving holes along said
upper edge and a pair of screw receiving holes along said lower edge, one of said
pair of bone screw receiving holes being adapted to position bone screws in a convergent
relationship to one another. The other of said pair of bone screw receiving holes
may be adapted to position bone screws in a divergent relationship to one another.
[0095] In a ninth aspect of the fifth further preferred embodiment of the present invention,
said implant further comprises at least one lock for retaining a bone screw within
said implant. Said at least one lock may retain a plurality of bone screws to said
implant.
[0096] In a tenth aspect of the fifth further preferred embodiment of the present invention,
said implant comprises one of bone and bone growth promoting material. Said bone growth
promoting material may be selected from one of bone morphogenetic protein, hydroxyapatite,
and genes coding for the production of bone.
[0097] In an eleventh aspect of the fifth further preferred embodiment of the present invention,
said implant comprises at least one of the following materials:
metal, titanium, plastic, and ceramic.
[0098] In a twelfth aspect of the fifth further preferred embodiment of the present invention,
said implant has an interior surface and a hollow defined therein, said hollow being
capable of containing bone growth promoting material. Said bone growth promoting material
may be selected from one of bone morphogenetic protein, hydroxyapatite, and genes
coding for the production of bone.
[0099] In a 13
th aspect of the fifth further preferred embodiment of the present invention, said implant
is in combination with a chemical substance to inhibit scar formation.
[0100] A sixth further preferred embodiment of the present invention is an interbody spinal
implant for insertion between adjacent vertebral bodies, comprising: opposed upper
and lower surfaces adapted to contact each of the adjacent vertebral bodies, respectively
from within the disc space; a leading end for insertion between the adjacent vertebral
bodies; and a trailing end opposite said leading end, said trailing end having an
exterior surface and an outer perimeter with an upper edge and a lower edge adapted
to be oriented toward the adjacent vertebral bodies, respectively; said outer perimeter
having at least one gap therein for permitting a portion of a bone screw to protrude
over the outer perimeter of said trailing end within a plane of said trailing end,
said gap being sufficient to retain a trailing end of the bone screw.
[0101] In a first aspect of the sixth further preferred embodiment of the present invention,
said implant is a fusion implant.
[0102] In a second aspect of the sixth further preferred embodiment of the present invention,
said trailing end is curved.
[0103] In a third aspect of the sixth further preferred embodiment of the present invention,
said implant has a height equal to the distance between the adjacent vertebral bodies
where installed into the disc space when installed.
[0104] In a fourth aspect of the sixth further preferred embodiment of the present invention,
at least one of said bone screw receiving holes passing through said exterior surface
and one of said edges is C-shaped in cross section.
[0105] In a fifth aspect of the sixth further preferred embodiment of the present invention,
at least one of said bone screw receiving holes passing through said exterior surface
and one of said edges has a partial circumference intersecting with the outer perimeter
of said trailing end.
[0106] In a sixth aspect of the sixth further preferred embodiment of the present invention,
said trailing end is relieved to allow for a head of a bone screw inserted into one
of said bone screw receiving holes to be at least partially recessed.
[0107] In a seventh aspect of the sixth further preferred embodiment of the present invention,
at least one pair of said plurality of bone screw receiving holes are adapted to orient
bone screws to be received therein at an angle to a horizontal mid-longitudinal plane
of said implant passing through said leading and trailing ends. Said plurality of
bone screw receiving holes may include a pair of screw receiving holes along said
upper edge and a pair of screw receiving holes along said lower edge, one of said
pair of bone screw receiving holes being adapted to position bone screws in a convergent
relationship to one another. The other of said pair of bone screw receiving holes
may be adapted to position bone screws in a divergent relationship to one another.
[0108] In an eighth aspect of the sixth further preferred embodiment of the present invention,
said implant further comprises at least one lock for retaining a bone screw within
said implant. Said at least one lock may retain a plurality of bone screws to said
implant.
[0109] In a ninth aspect of the sixth further preferred embodiment of the present invention,
said implant further comprises at least one bone screw having a leading end for placement
in the vertebral body and a trailing end opposite said leading end adapted to cooperatively
engage said implant so as to prevent the further advancement of the screw into the
bone and to be retained within one of said plurality of bone screw receiving holes
of said implant.
[0110] In a tenth aspect of the sixth further preferred embodiment of the present invention,
said implant comprises one of bone and bone growth promoting material. Said bone growth
promoting material may be selected from one of bone morphogenetic protein, hydroxyapatite,
and genes coding for the production of bone.
[0111] In an eleventh aspect of the sixth further preferred embodiment of the present invention,
said implant comprises at least one of the following materials:
metal, titanium, plastic, and ceramic.
[0112] In a twelfth aspect of the sixth further preferred embodiment of the present invention,
said implant has an interior surface and a hollow defined therein, said hollow being
capable of containing bone growth promoting material. Said bone growth promoting material
may be selected from one of bone morphogenetic protein, hydroxyapatite, and genes
coding for the production of bone.
[0113] In a 13
th aspect of the sixth further preferred embodiment of the present invention, said implant
is in combination with a chemical substance to inhibit scar formation.
[0114] Other embodiments of the invention will be apparent to those skilled in the art from
consideration of the specification and practice of the invention disclosed herein.
It is intended that the specification and examples be considered as exemplary only,
with a true scope of the invention being indicated by the following claims.